Powder for magnetic ferrite, magnetic ferrite, multilayer ferrite components and production method thereof

ABSTRACT

A multilayer ferrite component is produced with powder for magnetic ferrite, characterized by having the composition of Fe 2 O 3 : 40 to 51 mol %, CuO: 7 to 30 mol %, ZnO: 0.5 to 35 mol % and MgO: 5 to 35 mol %, in which a peak of particle size distribution positions in range of 0.3 to 1.2 μm. This MgCuZn ferrite uses such powders of less deterioration in a permeability μ and a peak position of particle size distribution in range of 0.3 to 1.2 μm, thereby enabling a co-firing together with Ag or Ag alloys. It is provided a magnetic ferrite of less deterioration in a magnetic characteristic, in particular a permeability μ against stress and enabling to be sintered at low temperature sintering, that is, below the melting points of Ag or Ag alloys used as electrode materials.

This application is a Divisional application of application Ser. No.09/734,202, now U.S. Pat. No. 6,533,956.

BACKGROUND OF THE INVENTION

The present invention relates to multilayer chip components such asmultilayer chip beads or multilayer chip inductors, magnetic ferrite andmultilayer ferrite components to be used to composite multilayercomponents represented by LC composite multilayer components, as well asa method for producing the same.

Multilayer chip ferrite components and composite multilayer components(called generically as “multilayer ferrite component or components” inthe present description) have been employed to various kinds ofelectric, electrical or electronic devices because of small volume andhigh reliability. The multilayer ferrite component is in generalproduced by laminating sheets or pastes for magnetic layers comprisingmagnetic ferrite and pastes for internal electrodes into a unitaryone-body through a thick film laminating technique, sintering it,printing or transcribing pastes for external electrodes on the surfaceof the sintered body, and carrying out a sintering thereon. By the way,the sintering after laminating in one body is called as a co-firing. Asa material for the internal electrode, Ag or Ag alloys are used becauseof low resistivity, and therefore as a magnetic ferrite material forcomposing magnetic layers, it is an absolute condition to enable theco-firing, in other words, enable the sintering at temperature belowmelting points of Ag or Ag alloys. Accordingly, for providing multilayerferrite components of high density and high magnetic characteristics, itwill be a key whether or not the magnetic ferrite can be sintered at thetemperature below the melting points of Ag or Ag alloys.

NiCuZn ferrite is known as the magnetic ferrite which can be sintered atthe temperature below the melting point of Ag or Ag alloys. In short,NiCuZn ferrite including powder of specific surface area rendered to beabout 6 m²/g or more by a milling can be sintered at the temperaturebelow the melting point of Ag (960° C.), and it has broadly been used tomultilayer ferrite components. However, since NiCuZn ferrite has themagnetic characteristic, particularly permeability μ which are sensitiveto external stress or thermal shock (refer to, for example, “Powder andPowder Metallurgy” vol. 39 & 8, pp. 612 to 617 (1992)), problems ariseas mentioned under during producing multilayer ferrite components. Thatis, the permeability μ is deteriorated by stress caused by barrelpolishing and plating in a producing procedure, stress caused bydifference in coefficients of linear expansion between the magneticlayers and the internal electrodes, and stress caused when mountingmembers on a base board, and inductance L is deviated from a designedvalue.

For solving the problems, two resolutions have been proposed. One ofthem is to face the magnetic layer and the internal electrodes to beopposite via a space therebetween (JP-A-4-65807). This proposal is toavoid the stress caused by the difference in the coefficients of thelinear expansion between the magnetic layers and the internalelectrodes. The other one is to cause Bi to exist in crystal grainboundaries of NiCuZn ferrite, thereby to generate tensile stress incrystal grains after sintering so as to make the sensitivity of themagnetic characteristic insensitive to the external stress(JP-A-10-223424). These two proposals were the effective measures fordeterioration of the magnetic characteristic of NiCuZn ferrite againstthe stress.

However, NiCuZn ferrite will be naturally an expensive material, becauseNiO as a raw material therefor is at high cost. Having paid attentionsto MgCuZn ferrite using MgO, Mg(OH)₂ or MgCO₃ which are cheaper thanNiO, there have been made various improvements. For example,JP-A-10-324564 proposes an amount of B (boron) to be 2 to 70 ppm inMgCuZn ferrite.

However, MgCuZn ferrite of this publication is sintered at 1200° C.according to examples, and it is difficult to apply this MgCuZn ferriteto the multilayer ferrite components directed by the invention. Becausethe co-firing cannot be carried out together with Ag or Ag alloys.

Japanese Patent No. 2,747,403 discloses the magnetic ferrite containingMgO, but does not refer to any sintering condition, and it is assumednot to satisfy the co-firing with Ag.

SUMMARY OF THE INVENTION

It is an object of the invention to offer magnetic ferrite of lessdeterioration of magnetic characteristic to stress, particularly ofpermeability μ, enabling the low temperature sintering, that is, tosinter at temperature below melting points of Ag or Ag alloys to be usedas materials for electrodes, and multilayer ferrite components employingsuch magnetic ferrite. It is another object of the invention to offer amethod of producing magnetic ferrite and multilayer ferrite components.

Powder for magnetic ferrite of the invention has the composition ofFe₂O₃: 40 to 51 mol %, CuO: 7 to 30 mol %, ZnO: 0.5 to 35 mol % and MgO:5 to 35 mol %, in which a peak position of particle size distributionranges 0.3 to 1.2 μm. In powder for magnetic ferrite, one part of MgOmay be replaced with NiO. Actually, a total amount of MgO and NiO isenough with 5 to 35 mol %.

Powder for magnetic ferrite of the invention has the composition ofFe₂O₃: 40 to 51 mol %, CuO: 7 to 30 mol %, ZnO: 0.5 to 35 mol % and MgO:5 to 35 mol %, and is sintered at temperature below 940° C. Depending onthis magnetic ferrite, the sintering is available at temperature below940° C., and it is possible to obtain multilayer ferrite components ofsatisfied properties.

When the magnetic ferrite of the invention is sintered at temperaturerange of 940° C. or lower, a shrinkage is 10% or higher. This fact showsthat the sintering below 940° C. is possible.

In the magnetic ferrite of the invention, the composition is desirableto be Fe₂O₃: 45 to 49.8 mol %, CuO: 8 to 25 mol %, ZnO: 15 to 25 mol %and MgO: 7 to 26 mol %.

The multilayer ferrite component of the invention uses the magneticferrite mentioned above and has external electrodes electricallyconnected to the internal electrodes which are alternately multilayerwith the magnetic ferrite layer, said magnetic ferrite layer beingcomposed of the sintered magnetic ferrite of Fe₂O₃: 40 to 51 mol %, CuO:7 to 30 mol %, ZnO: 0.5 to 35 mol % and MgO: 5 to 35 mol % and also theinternal electrodes being composed of Ag or Ag alloys.

The multilayer ferrite component of the invention has the alternatelamination of the dielectric layers and the internal electrodes, and maybe integrally composed with the multilayer capacitor components havingexternal electrodes electrically connected to the internal electrodes.In short, the composite multilayer components such as LC compositemultilayer components are also defined as the multilayer ferritecomponents in the invention.

The multilayer ferrite component of the invention has the alternatelamination of the magnetic ferrite layers and the internal electrodelayers and has external electrodes electrically connected to theinternal electrodes, said magnetic ferrite layer being composed of thesintered ferrite of magnetostriction being 10×10⁻⁶ or lower, and saidinternal electrode being composed of Ag or Ag alloys. In this multilayerferrite components, it is preferable that the sintered ferrite is MgCuZnbased ferrite having the composition of Fe₂O₃: 40 to 51 mol %, CuO: 5 to30 mol %, ZnO: 0.5 to 35 mol % and MgO: 5 to 50 mol %.

The multilayer ferrite component of the invention is integrally unitedof inductor components having the alternate laminations of the magneticferrite layers and the internal electrode layers and capacitorcomponents having the alternate laminations of the dielectric layers andthe internal electrodes, and has the external electrode electricallyconnected to the internal electrode of the multilayer inductors and themultilayer capacitors. The magnetic ferrite layer of the multilayerinductor components is composed of the sintered MgCuZn based ferrite ofthe magnetostriction being 10×10⁻⁶ or lower, and the internal electrodeis composed of Ag or Ag alloys. In this multilayer ferrite components,it is preferable that the sintered MgCuZn based ferrite is MgCuZn basedferrite having the composition of Fe₂O₃: 45 to 49.8 mol %, CuO: 7 to 30mol %, ZnO: 15 to 25 mol % and MgO: 5 to 35 mol %. Further, one part ofMgO may be replaced with NiO. Actually, the composition has Fe2O3: 45 to49.8 mol %, CuO: 7 to 30 mol %, ZnO: 15 to 25 mol % and MgO+NiO: 5 to 35mol %.

The method of producing the magnetic ferrite comprises, according to theinvention, a step of mixing raw powders, a step of pre-sintering themixed raw powders at temperature of below 900° C., a step of milling thepre-sintered material, a step of pressing into a desired with shapepowders of a peak in the distribution being 0.3 to 1.2 μm, selected fromthe milled powders, and a step of sintering the pressed bodies.

In the above magnetic ferrite producing method, the magnetic ferrite maybe MgCuZn based ferrite where the raw powders are one or two or more ofMg, Mg(OH)₂ and MgCO₃, Fe₂O₃ powder, CuO powder and ZnO powder. In sucha case, an addition amount of CuO powder is desirably 5 to 25 mol %.

The method of the invention of producing the multilayer ferritecomponents having the multilayer magnetic layers and internalelectrodes, comprises mixing raw powders of the magnetic ferrite,pre-sintering the mixed raw powders at temperature of below 900° C.,milling the pre-sintered material, selecting such powders of a peak inthe distribution of the particle size being 0.3 to 1.2 μm from themilled powders, and subsequently comprises a step of making sheets orpastes for forming the magnetic layers with said powders of particlesize distribution peak ranging 0.3 to 1.2 μm, a step of alternatelylaminating said sheets or pastes and a material for internal electrodesfor forming a multilayer body, and a step of sintering said multilayerbody at temperature of 940° C. or lower.

In the above multilayer ferrite producing method, the materials for theinternal electrode may be Ag or Ag alloys. The sintering temperature isdesirable at 870 to 930° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematically cross sectional view of the multilayer chipinductor;

FIG. 2 is a cross sectional view along II—II;

FIG. 3 is a cross sectional view of LC composite component according tothe embodiment;

FIG. 4 is a graph showing the stress dependence of the permeability μ ofMgCuZn ferrite and NiCuZn ferrite;

FIG. 5 is a graph showing the stress dependence of the permeability μ ofMgCuZn ferrite and NiCuZn ferrite;

FIG. 6 is a graph showing the effect of CuO contents on thedensification characteristics;

FIG. 7 is a graph showing the particle size distribution measured in theExample 3;

FIG. 8 is a graph showing the effect of the peak positions in particlesize distribution on the densification characteristics; and

FIG. 9 is a graph showing the effect of the pre-sintered temperature onthe densification characteristics.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed explanation will be made to the invention.

First reference will be made to a cause in which the lower themagnetostriction, the smaller change of the permeability μ by stress.

MgCuZn ferrite and NiCuZn ferrite were used to observe deterioration ofthe permeability μ by stress. As a result, It was confirmed that MgCuZnferrite was less than NiCuZn ferrite in the change of the permeabilityμ. By the way, an initial permeability (μi) is known to be defined bythe following formula. From this formula, it may be said that the lessthe magnetostriction of the material, the easier the deterioration ofthe permeability μ is restrained.

μi=AMs2/(ak 1 +bλsσ)

(Ms=saturated flux density, K=anisotropic constant λs=magnetostriction,σ=stress).

When a comparison of the magnetostriction is made to MgCuZn ferrite andNiCuZn ferrite, MgCuZn is smaller. Although the magnetostriction isvaried depending on compositions, the magnetostriction of NiCuZn ferriteexceeds 10×10⁻⁶, while that of MgCuZn ferrite shows values below10×10⁻⁶. From this, it is imagined that if MgCuZn ferrite is used, itcauses to lower the change of the permeability μ by stress.

Proposals have conventionally been made, as disclosed in JP-A-4-65807,that the magnetic layer and the internal electrode are faced via a spacefor reducing stress from the internal electrode, otherwise asJP-A-10-223414, Bi is caused to intervene at crystal grain boundariesfor reducing stress from the grain boundaries. In short, theconventional proposals were to lessen the item of stress (σ) of theabove formula for avoiding deterioration of the permeability.

In contrast, whereas the invention is to use a material of smallmagnetostriction (λs) for avoiding deterioration of the permeability, itmay be said that the invention is based on a different technical thoughtfrom that of the prior art. Moreover, MgCuZn ferrite can be produced atlower cost than in NiCuZn ferrite, and this is one of large merits forparts of electronic devices or electronic instruments fartherprogressing cost-down.

Herein, an obstacle is that the low temperature sintering using theconventional MgCuZn ferrite is difficult. An inventor made thereuponinvestigations for carrying out the low temperature sintering of MgCuZnferrite, and found that it was useful to control the pre-sinteringtemperature of raw powder to be low, specifically to be 850° C. orlower, and further found that it was important to regulate distributionof milled powder after pre-sintering, specifically to use powder of thedistributing peak of its diameter being positioned at 0.3 to 1.2 μm. Itwas clarified that if preparing the conditions of the pre-sinteringtemperature and the particle size distribution as mentioned above,MgCuZn ferrite could be sintered at low temperature, that is, 940° C. orlower, as securing sufficient characteristics.

The invention employs MgCuZn ferrite as the magnetic ferrite. As anactual embodiment of MgCuZn based ferrite, there exists MgCuZn ferrite.For realizing MgCuZn ferrite, it is sufficient to make raw powders ofone or two kinds or more of MgO, Mg(OH)₂ and MgCO₃, Fe₂O₃ powder, CuOpowder and ZnO powder. The composition (addition amount) therefor may beselected in view of a desired magnetic characteristic and otherpurposes, and basically the following ranges are satisfied. Fe₂O₃: 40 to51 mol %, CuO: 5 to 30 mol %, ZnO: 0.5 to 35 mol %, and one or two kindsor more of MgO, Mg(OH)₂ and CO₃: 5 to 50 mol %.

In the invention, one part of Mg of MgCuZn ferrite may be replaced withNi. In other words, the invention may use MgNiCuZn ferrite as MgCuZnbased ferrite. In this case, NiO is added as raw powder, and may beadded together with one or two kinds or more of MgO, Mg(OH)₂ and MgCO₃,ranging 5 to 50 mol % in total.

The magnetic characteristic of the magnetic ferrite has a very strongdependency on the composition, and in ranges out of the abovecomposition, the permeability μ or the quality coefficient Q arelowered, and such magnetic ferrite is not suited for the multilayerferrite components.

An embodiment of the invention will be described hereinafter.

The amount of Fe₂O₃ gives large influences to the permeability. If Fe₂O₃is less than 40 mol %, the permeability is small, and as coming near toa stoichiometric composition as ferrite, the permeability goes upward,but rapidly goes down after a peak of the stoichiometric composition.Accordingly, an upper limit is 51 mol %. A preferable amount of Fe₂O₃ is45.0 to 49.8 mol %.

CuO is a compound contributing to lowering of the sintering temperature,and being less than 7 mol %, the low temperature sintering below 940° C.cannot be realized. But being more than 30mol %, a resistivity of thesintered body of ferrite is decreased and the quality coefficient Q isdeteriorated, and so CuO ranges 7 to 30 mol %, preferably 8 to 25 mol %.

ZnO can heighten the permeability μ as increasing its amount, but beingtoo much, a Curie temperature is lower than 100° C., so that thetemperature characteristic demanded to electronic components cannot besatisfied. Therefore, the amount of ZnO ranges 0.5 to 35 mol %,preferably 15 to 25 mol %.

MgO is effective to decrease magnetostriction. For providing thiseffect, the amount of 5 mol % or higher is necessary. But since thepermeability μ trends to go down as increasing the amount of MgO, anupper limit is 35 mol % or lower. A preferable amount ranges 7 to 26 mol%. In the magnetic ferrite and the powder for the magnetic ferrite ofthe invention, one part of MgO can be replaced with NiO, and theaddition in such a case is 5 to 35 mol % in total with MgO, desirably 7to 26 mol %. When replacing one part of MgO with NiO, the amount of NiOis preferably 70% or lower of said total amount. Because, exceeding 70%,the magnetostriction of the magnetic ferrite to be obtained is large, sothat it is not easy to get the effect of avoiding deterioration of thepermeability μ. Further, Mg(OH)₂ and MgCO₃ may be used together with MgOor in place of MgO.

The magnetic characteristic of the magnetic ferrite has a very strongdependency on the composition, and in ranges out of the abovecomposition, the permeability μ or the quality coefficient Q are small,and such magnetic ferrite is not suited as the multilayer ferritecomponents.

Incidentally, for producing the multilayer ferrite components of theinvention, the co-firing is necessary. The co-firing should be carriedout at temperature below 940° C., taking the melting points of Ag or Agalloys to be internal electrodes into consideration. Therefore, it isimportant that the peak position in distribution of powder for themagnetic ferrite before sintering ranges 1.2 μm or lower. The inventormade studies on the low temperature sintering of MgCuZn ferrite, andfound that if the peak of distribution of powder before sintering waspositioned 1.2 μm or lower, the low temperature sintering was possibleto MgCuZn ferrite which was conventionally difficult to be sintered atlow temperature, and also found that it was useful for obtaining powderof such distribution to control the temperature of pre-sintering to beat 900° C., desirably 850° C. or lower. It was clear that if providingthe above mentioned conditions of the pre-sintering temperature and theparticle size distribution, MgCuZn ferrite could be sintered at lowtemperature as 940° C. or lower as securing the sufficientcharacteristics.

For obtaining powder for the magnetic ferrite of the invention, thepre-sintering temperature is to be 900° C. or lower, thereby enablingthe low temperature sintering. Because, exceeding 900° C., thepre-sintered material is hardened, it is difficult to provide thedistribution of powders enabling the low temperature sintering. Thepreferable temperature for pre-sintering is 730 to 850° C.

The pre-sintered material is milled, and the milled powder is sintered.It is important to the invention that the peak of the particle sizedistribution is positioned in the range of 0.3 to 1.2 μm. Exceeding 1.2μm, the low temperature sintering, i.e., the sintering below 940° C. isdifficult. Reversely, being 1.2 μm or smaller, the shrinkage percentagein the sintering at temperature of 940° C. or lower can be secured to be10% or more, so that the magnetic ferrite having enough characteristicscan be obtained. But, being less than 0.3 μm, a specific surface area islarge, and it is difficult to obtain pastes or sheets for getting themultilayer ferrite components. The desirable peak position of theparticle size distribution is 0.5 to 1.0 μm. For obtaining powder ofsuch distribution, the milling condition should be controlled, but it isalso possible to collect powder of such distribution from milled powdernot depending on controlling of the conditions.

The magnetic ferrite powders of the invention are mixed powders of MgOpowder, Fe₂O₃ powder, CuO powder and ZnO powder. When replacing one partof MgO with NiO, NiO powder is also mixed. When Mg(OH)₂ or MgCO₃ is usedtogether with MgO or in place of MgO, it is sufficient to mix Mg(OH)₂ orMgCO₃. For more accelerating the low temperature sintering, variouskinds of glasses such as boro-silicate glass or oxides of low meltingpoints such as V₂O₅, Bi₂O₃, B₂O₃, WO₃ or PbO may be added.

Next reference will be made to the multilayer chip inductor which is oneembodiment of the multilayer ferrite components. FIG. 1 is aschematically cross sectional view of the multilayer chip inductor, andFIG. 2 is a cross sectional view along II—II of FIG. 1. The multilayerchip inductor 1 is, as seen in FIG. 1, composed of a chip body 4 ofmulti-structure having alternate laminations of the magnetic ferritelayers 2 and the internal electrodes 3, and the external electrodes 5disposed at both edges of the chip body 4 for electrically conductingthe internal electrode 3.

The magnetic ferrite material of the invention is used to the magneticferrite layers 2. That is, the powder of the distribution peak ranging0.3 to 1.2 μm is mixed with a binder and a solvent to provide pastes forforming the magnetic ferrite layers 2. This paste and a paste forforming the internal electrode 3 are alternately printed, multilayer andsintered so as to produce the chip body 4 of one-body.

For the binder, known binders as ethyl cellulose, acrylic resin orbutyral resin may be used. For the solvent, known terpineol, butylcarbitol, or kerosene are available. The addition amounts of the binderand the solvent are not limited. But, ranges of 1 to 5 weight percentsas the binder and 10 to 50 weight percents as the solvent arerecommended.

Other than the binder and the solvent, dispersant, plasticizer,dielectric, and insulator may be added 10 weight percents or lower. Asthe dispersant, sorbitane fatty acid ester or glycerine fatty acid estermay be added. As the plasticizer, dioctylbphthalate, di-n-butylphthalate, butyl phthalyl glycolic acid butyl may be added.

The magnetic ferrite layer 2 can be formed with a sheet therefor.Namely, the powder of the distribution peak ranging 0.3 to 1.2 μm ismixed with the binder of a main component being polyvinyl butyral andthe solvent as toluene or xlylene for getting a slurry. The slurry iscoated on a film as polyester film by, e.g., a doctor blade method, anddried to obtain the sheet for the magnetic ferrite layer 2. The sheetsare alternately multilayer with the pastes for the internal electrode 3and sintered, and the chip body 4 of multi-layered structure can beprovided. The amount of the binder is not limited, but the range of 1 to5 weight percents is recommended. Further, the dispersant, plasticizer,dielectric, and insulator may be added at 10 weight percents or lower.

With respect to the internal electrodes 3, it is preferable to employ Agor Ag alloys having small resistivity, e.g., Ag—Pd alloy for providingthe quality coefficient Q practicable as the inductor, but not limitingthereto but enabling to use Cu, Pd or their alloys. The paste forobtaining the internal electrodes 3 is obtained by mixing and kneadingpowders of Ag or Ag alloys or their oxide powders with the binder andthe solvent. For the binder and the solvent, the same as that used forforming the magnetic ferrite layer 2 may be applied. The internalelectrode layers 3 are each elliptical and each of the adjacent layersis, as shown in FIG. 3, spiral for securing the electric conductivityand composing a closed magnetic circuit coil (coil pattern).

Materials for the external electrode 5 are known materials such as Ag,Ni, Cu, or Ag—Pd alloy. The external electrode 5 is formed with thesematerials by a printing method, plating method, vapor deposition method,ion plating method or spattering method.

No especial limitation is made to outer diameters and dimensions of thechip 4 of the multilayer chip inductor 1. Appropriate selection isdecided depending on usage. In general, outward configurations aresubstantially rectangular parallelepiped, and many dimensions are 1.0 to4.5 mm×0.5 to 3.2 mm×0.6 to 1.9 mm. Space t1 between electrodes andthickness t2 of a base of the magnetic ferrite layer 2 are notespecially limited. The space t1 may be determined to be 10 to 100 μmand the thickness t2 may be 250 to 500 μm, and further, the thickness t3of the internal electrode 3 itself ranges ordinarily 5 to 30 μm, pitchesof coiling pattern are 10 to 100 μm, and the coiling number is around1.5 to 20.5 turns.

The sintering temperature after alternately laminating the pastes orsheets for the magnetic ferrite layers 2 and the pastes for the internalelectrodes 3 is determined to be 940° C. or lower. Because being higherthan 940° C., materials composing the internal electrode 3 in themagnetic ferrite layer 2 are diffused and the magnetic characteristic isremarkably reduced. Although the magnetic ferrite is suited to the lowtemperature sintering, a sintering at temperature of less than 800° C.is not sufficient. Therefore, the sintering is desirable at temperatureof 800° C. or higher. A desirable sintering temperature ranges 820 to930° C., more desirable is 875 to 920° C. The sintering time is 0.05 to5 hours, desirably 0.1 to 3 hours

Further explanation will be made to LC composite components being oneembodiment of the multilayer LC composite components. FIG. 3 is aschematically cross sectional view of LC composite component.

As shown in FIG. 3, the LC composite component 11 is composed by unitinga chip capacitor 12 and a chip ferrite component 13.

The chip capacitor 12 has a multi-layered structure of alternatelylaminating ceramic dielectric layers 21 and internal electrodes 22. Nolimitation is made to the ceramic dielectric layer 21, and knownexisting dielectric materials may be employed therefor. In theinvention, titanium oxide of the low sintering temperature is desirable,and titanic acid based composite oxides, zirconic acid based compositeoxides, or their mixture may be used. For decreasing temperature,various kinds of glasses such as boro-silicate glass may be added. Asthe internal electrode 22, the same material as the internal electrode 3of the multilayer chip inductor 1 can be used as mentioned above. Theinternal electrode 22 is electrically connected alternately to otherexternal electrodes.

The chip ferrite component 13 is composed of the multilayer chipinductor 1 having the alternate lamination of the magnetic ferrite layer32 and the electrode layers 33. This structure is the same as themultilayer chip inductor 1 mentioned above. Therefore, a detailedexplanation will be omitted herein.

No limitation is made to outer diameters and dimensions of the LCcomposite component 11 as explained in the multilayer chip inductor 1.Accordingly, appropriate selection is decided depending on usage. Ingeneral, outward configurations are almost rectangular parallelepiped,and dimensions are 1.6 to 10.0 mm×0.8 to 15.0 mm×1.0 to 5.0 mm.

EXAMPLES

The invention will be explained by way of Examples.

Example 1

The magnetic ferrite materials were produced with the mixed compositionshown in Table 1 and under the following producing conditions.Measurements were made on the permeability μ, the stress resistivitycharacteristic, the magnetostriction and the density of the producedmagnetic ferrite. The results of the permeability μ, themagnetostriction and the density are shown in Table 2 and the stressresistivity characteristic is shown in FIG. 4.

Producing Conditions

The raw powder was weighed in accordance with table 1 and mixed to wetmixture in the ball mill consist of stainless steel pot and steel ballmedia for 16 hours (the dispersant was a pure water). After the mixturewas completed, the mixed powder was dried by the spray dryer, followedby the pre-sintering at 760° C. for 10 hours. After the pre-sintering,the sintered powder was milled for 66 hours in the ball mill, and themilled powder was sintered to produce the sintered body of toroidal andrectangular paralelopiped shapes. The sintering temperature was 900° C.and the holding time was 2 hours.

The measuring method of each of characteristics is as follows.

Magnetostriction

The test samples of 5×5×20 mm were measured with the saturatedmagnetostriction measuring apparatus made by Naruse Scientific MachineryCo., Ltd.

Particle Size Distribution

The powder of 0.02 g to be measured in distribution was dispersed in thewater of 100 ml. The measuring path of the particle size distributinggauge was washed away, and the reference of the particle size diameterdistributing gauge was measured for measuring the particle sizedistribution. The dispersion and distribution of the powder weremeasured with the Helos System of Sympatec Inc.

The particle size distribution and frequency were calculated with theprogram of the particle size distribution gauge through the laserdiffraction method.

Permeability

The sample of toroidal shape was wound 20 turns with the copper madewire (diameter: 0.35 mm), and inductance was measured at the measuringfrequency of 100 kHz and the current of 0.2 mA with LCR meter (made byHewlett Packard Inc.), and the permeability was demanded by thefollowing formula.

Permeability μ=(le×L)/(μ0×Ae×N²)

herein, le: Length of the magnetic path,

L: Inductance of the sample,

μ0: Permeability of vacuum=4π×10⁻⁷ (H/m),

Ae: Cross sectional area of the sample, and

N: winding number of the coil.

Stress Resistance Characteristic

The sample of square toroidal shape was wound 20 turns with the coppermade wire (diameter: 0.35 mm), and connected to LCR meter (made byHewlett Packard Inc.). Under this condition, the decreasing rate of theinductance was measured under the conditions of the measuring frequencyof 100 kHz and the current of 0.2 mA, while loading by the bendingresistance strength tester. For comparing with the decreasing rate ofthe permeability μ, the decreasing rate of the inductance is shown asthe permeability μ in FIGS. 4 and 5.

TABLE 1 mol % Sorts of No. Fe₂O₃ NiO MgO CuO ZnO Ferrites 1 49 14.0 —9.5 27.5 NiCuZn 2 49 21.0 — 9.0 21.0 NiCuZn 3 49 — 14.0 9.5 27.5 MgCuZn4 49 — 21.0 9.0 21.0 MgCuZn 5 49  7.0  7.0 9.6 21.0 MgNiCuZn

TABLE 2 Multilayer ferrite chip Sintered materials inductor A (× BDensity Inductance C No. 10⁻⁶) (μ) (g/cm³) (μH) (Q) 1 12.0 279 4.91 5.639.0 2 18.0 107 4.81 2.5 38.5 3 3.0 240 4.64 7.2 41.0 4 3.2 104 4.75 3.240.7 5 7.0 260 4.78 6.2 41.0 A: Magnetostriction B: Permeability C:Quality coefficient

From Tables 1 and 2, the following was found.

Nos. 3 and 1 are different in that No. 3 is added with MgO of 14 mol %and No. 1 is added with NiO of 14 mol %, but the other elements are thesame. Comparing both magnetostrictions (λs), No. 3 is 3×10⁻⁶, while No.1 is 12×10⁻⁶. That is, it is seen that MgCuZn ferrite is smaller thanNiCuZn ferrite in the magnetostriction. This face can be comprehendedfrom the magnetostrictions of Nos. 4 and 2 which are the same elementsexcept MgO and NiO.

Further, comparing Nos. 1 and 2, the magnetostrictions are largelychanged from 12×10⁻⁶ to 18×10⁻⁶ by increasing the content of NiO from 14mol % to 21 mol %. In contrast, comparing Nos. 3 and 4, though MgOincreases from 14 mol % to 21 mol %, the magnetostriction only changesfrom 3×10⁻⁶ to 3.2×10⁻⁶. In short, it may be understood even if thecontent of MgO increases, basically it does not make themagnetostriction large.

No. 5 is an example where NiO was added together with MgO, and comparingNos. 1 and 2, the magnetostriction is small and the permeability μ has agood value.

FIG. 4 shows the stress resistance characteristics of Nos. 3 and 1, andFIG. 5 shows those of Nos. 4 and 2. From FIGS. 4 and 5, it can beunderstood that the permeability μ is deteriorated by giving stress.However, it is seen from FIG. 4 that the deterioration degree of thepermeability μ is smaller in No. 3 (3×10⁻⁶) of the smallmagnetostriction than No. 1 (12×10⁻⁶) of the large magnetostriction. Thesame is applied to FIG. 5. Accordingly, for reducing the deteriorationdegree of the permeability μ by stress, it is advantageous to employMgCuZn based ferrite of small magnetostriction.

To 100 weight percents of the powder having the composition in Table 1,added were 2.5 weight percents of ethyl cellulose and 40 weight percentsof terpineol, and those were mixed by a three-roll-mill for preparingthe pastes for the magnetic ferrite layers. On the other hand, to 100parts of Ag of the average powder being 0.8 μm, added were 2.5 weightpercents of ethyl cellulose and 40 weight percents of terpineol, andthose were mixed by the three-roll-mill for preparing the pastes for theinternal electrodes. The pastes for the magnetic ferrite layers and thepastes for the internal electrode layers were printed and alternatelymultilayer, and sintered at 900° C. for 2 hours for providing themultilayer chip inductors as shown in FIGS. 1 and 2. The dimension ofthe multilayer chip inductor 1 of 2012 type is 2.0 mm×1.2 mm×1.1 mm, andthe coil windings are 4.5 turns. The multilayer chip inductor 1 wasfired at its edges with the external electrodes 5 at 600° C.

With respect to the obtained multilayer chip inductor 1, the inductanceL and the quality coefficient Q were measured at the measuring frequencyof 100 kHz and the measuring current 0.2 mA and with the LCR meter (madeby Hewlett Packard Inc.).

The results are shown in Table 2. If either of MgCuZn ferrite andMgNiCuZn ferrite was used, the equivalent characteristics could beobtained to those of the multilayer chip inductor using the conventionalNiCuZn ferrite.

Example 2

The Example 2 was to confirm influences given by the content of CuO. Thesamples were made with the mixing elements shown in Table 3 and underthe same conditions as those of the Example 1, and the permeability μand the density were measured. The results are shown in Table 4.

TABLE 3 mol % Sorts of No. Fe₂O₃ NiO MgO CuO ZnO Ferrites 6 49 — 23.54.0 23.5 MgCuZn 7 49 — 21.5 8.0 21.5 MgCuZn 8 49 — 19.5 12.0 19.5 MgCuZn9 49 — 17.5 16.0 17.5 MgCuZn 10 49 — 15.5 20.0 15.5 MgCuZn 11 49 — 13.524.0 13.5 MgCuZn 12 49 — 11.5 28.0 11.5 MgCuZn

TABLE 4 Multilayer ferrite chip Sintered materials inductor Remarks BDensity Inductance C CuO No. (μ) (g/cm³) (μH) (Q) (mol %) 6 40 3.87 1.020.0 4.0 7 180 4.66 4.6 38.0 8.0 8 210 4.75 5.4 39.0 12.0 9 224 4.80 5.740.0 16.0 10 218 4.81 5.6 39.3 20.0 11 200 4.83 5.1 38.4 24.0 12 1004.85 2.6 24.4 28.0 B: Permeability C: Quality coefficient

From Tables 3 and 4, it is seen that the permeability μ is improved asincreasing the amount of CuO, but exceeding more than 24 mol %, itlargely goes down. When CuO is 4.0 mol %, a practically sufficientmagnetic characteristic cannot be provided, and if being 28.0 mol %, themagnetic permeability is worsened. In view of the magneticcharacteristic, the CuO amount is desirably 5 mol % to 25 mol %.

In Table 3, with respect to No. 6 (CuO: 4.0 mol %), No. 7 (CuO: 8.0 mol%), No. 8 (CuO: 12.0 mol %), No. 9 (CuO: 16.0 mol %), and No. 11 (CuO:24.0 mol %), the milled pre-sintered powder was heated up to apredetermined temperature and the shrinkage percentage (ΔL/L) wasmeasured. The shrinkage percentage serves as a standard for easysintering, and it will be able to regarded that the larger the shrinkagepercentage, the easier the sintering. The results are shown in FIG. 6.The lines of FIG. 6 are called as the heat shrinking curves. From FIG.6, it is seen that the shrinkage percentage becomes larger as the CuOamount increases. That is, by the CuO-addition, the sintering was madeeasy and the sintering at lower temperature was available.

When comparing No. 9 (CuO: 16.0 mol %) and No. 11 (CuO: 24.0 mol %), itis comprehended that CuO is enough with around 20.0 mol %. On the otherhand, No. 6 (CuO: 4.0 mol %) is smaller than No. 7 (CuO: 8.0 mol %) inthe shrinkage percentage, and for fully enabling the low temperaturesintering, CuO should be 7 mol %, more preferably 10.0 mol % or high.

The multilayer chip inductor was made similarly to the Example 1, andthe inductance L and the quality coefficient Q were measured as wellsimilarly thereto. The results are shown in Table 4. Also in themultilayer chip inductor, it was confirmed that the good inductance Land the good quality coefficient Q were obtained in the example whereCuO was 8.0 to 24.0 mol %.

Example 3

The Example 3 was to confirm influences given by the pre-sinteringtemperature. The samples were made with the mixing elements shown inTable 5 and under the same conditions as those of the Example 1 (thesintering temperature 900° C.), except that the pre-sinterings werecarried out at various temperatures and the permeability μ and thedensity were measured similarly to the Example 1. Table 6 shows themeasured results of the permeability μ and the density per each ofpre-sintering temperatures.

TABLE 5 mol % Sorts of No. Fe₂O₃ NiO MgO CuO ZnO ferrites 49 — 19.5 11.020.5 MgCuZn

TABLE 6 Multilayer ferrite Pre-sintering- Sintered materials chipinductor temperature B Density Inductance C No. (° C.) (μ) (g/cm³) (μH)(Q) 13 700 100 4.41 2.6 38.5 14 730 108 4.43 2.8 38.4 15 760 115 4.582.9 39.0 16 790 119 4.61 3.0 40.0 17 810 136 4.65 3.5 40.2 18 850 1284.63 3.3 39.2 19 900 94 4.14 2.4 20.0 B: Permeability C: Qualitycoefficient

As the general tendency, until the range where the sintering temperatureis 850° C., when temperature becomes higher, the permeability μ and thedensity become higher. This means that effects of the pre-sintering isexhibited as increasing of the pre-sintering temperature. When thetemperature is high as 900° C., the permeability μ and the densitydecrease.

The raw powder having the mixed elements shown in Table 5 waspre-sintered at 850° C., and two kinds of powders shown in FIG. 7 wasobtained by changing the milling condition.

By using the two kinds of powders, the heat-shrinking curves were soughtfor observing influences given to the sintering by the peak position ofthe particle size distribution. The results are shown in FIG. 8.

It is seen that the powder of the peak position of the distributionbeing 0.62 μm is larger in the shrinkage percentage than the powder of1.38 μm in the range of 750 to 1000° C. It may be said that the largerthe shrinkage percentage, the more easily the sintering progresses, andso it is seen that the powder of peak position being 0.62 μm is moreexcellent in the sinterability than the powder of 1.38 μm.

In the invention, for enabling to co-firing with Ag or Ag alloys formingthe internal electrode, it is required as mentioned above to perform thesintering at the low temperature of 940° C. or lower. On the other hand,the powder of the distribution peak being 0.62 μm is larger than thepowder of 1.38 μm in the shrinkage percentage at temperature of 940° C.or lower and may be said to be suited to the low temperature sintering.

In FIG. 6, with respect to No. 15 (pre-sintering temperature: 760° C.),No. 18 ( pre-sintering temperature: 850° C.), and No. 19 (pre-sinteringtemperature: 900° C.), the shrinkage percentages were measured when themilled powders after pre-sintering were heated at predeterminedtemperatures. The results are shown in FIG. 9. Among the threepre-sintering temperatures, No. 18 of 850° C. shows the largestshrinkage percentage and is suited to the low temperature sintering. No.19 of pre-sintered at 900° C. shows that the pre-sintered powder was toohard and the milling was not complete, so that it is assumed that theshrinkage percentage was smaller than No. 18. In No. 15 of 760° C., thesingle phase structure of spinel was not obtained by pre-sintering, sothat it is assumed that the shrinkage percentage by heating was inferiorto that of No. 18. According to other studies, it was confirmed that thesingle structure of spinel could be obtained by pre-sintering attemperature of 800° C. or higher. It is therefore important to take thispoint into consideration for determining the pre-sintering temperature.

The multilayer chip inductor was made similarly to the Example 1, andthe inductance Land the quality coefficient Q were measured as wellsimilarly thereto. The results are shown in Table 6. Also in themultilayer chip inductor, it was confirmed that the good inductance Land the good quality coefficient Q were obtained at temperature of 850°C. or lower, but at 900°, the inductance L and the quality coefficient Qabruptly dropped.

Example 4

The Example 4 was to confirm influences given by the sinteringtemperature. The samples were made with the mixing elements shown inTable 7 and under the same conditions as those of the Example 1 (thepre-sintering temperature 760° C.), except that the sintering werecarried out at various temperatures and the permeability μ and thedensity were measured similarly to the Example 1. Table 8 shows themeasured results of the permeability μ and the density per each of thepre-sintering temperatures. The multilayer chip inductance was madesimilarly to the Example 1 and the inductance L and the qualitycoefficient Q were measured similarly to the Example 1. The results areshown in Table 8.

TABLE 7 mol % Sorts of No. Fe₂O₃ NiO MgO CuO ZnO ferrites 49.5 — 13.311.0 26.2 MgCuZn

TABLE 8 Multilayer ferrite Sintering Sintered materials chip inductortemperature B Density Inductance C No. (° C.) (μ) (g/cm³) (μH) (Q) 20850 60 4.28 1.5 21.0 21 870 131 4.60 3.4 37.0 22 890 266 4.74 6.8 40.023 910 420 4.75 10.8 40.5 24 930 702 4.96 18.0 41.0 25 950 831 5.01 0.10.1 B: Permeability C: Quality coefficient

In Table 8, the permeability μ of the density of the sintered materialsare improved as the sintering temperature becomes higher. So, seeingthese results only, a selection of high temperature is desirable.However, the inductance L and the quality coefficient Q abruptly drop at950° C. sintering. This is because Ag composing the internal electrodeis diffused in the magnetic ferrite layer. Accordingly, when producingmultilayer ferrite components using Ag or Ag alloys as the materials ofthe internal electrode, the sintering should be carried out attemperature of less than 950° C.

As mentioned above, according to the invention, it is possible toproduce the magnetic ferrite of less deterioration in the permeability μto stress and enabling to be sintered at low temperature sintering, thatis, below the melting points of Ag or Ag alloys using as the materialsof electrode, and the multilayer ferrite components at low cost.

What is claimed is:
 1. Multilayer ferrite components comprising: aplurality of magnetic ferrite layers and internal electrodes which arealternately laminated each other; external electrodes electricallyconnected to said internal electrodes; wherein said magnetic ferritelayer is composed of sintered magnetic ferrite having the composition ofFe₂O₃ of 40 to 51 mol %, CuO of 7 to 25 mol %, ZnO of 0.5 to 35 mol %and MgO: 5 to 35 mol %, and the internal electrode is composed of Ag orAg alloys.
 2. Multilayer ferrite components as set forth in claim 1,wherein the multilayer ferrite component is united one-body compositewith multilayer capacitor components which has an arrangement ofalternately laminating dielectric layers and internal electrodes, andexternal electrodes electrically connected to the internal electrodes.3. Multilayer ferrite components comprising: a plurality of magneticferrite layers and internal electrodes which are alternately laminatedeach other; external electrodes electrically connected to said internalelectrodes; wherein said magnetic ferrite layer is composed of sinteredmagnetic ferrite of megnetostriction being 10×10⁻⁶ or lower, saidinternal electrode is composed of Ag or Ag alloys.
 4. The multilayerferrite components as set forth in claim 3, wherein said sinteredmagnetic ferrite layer is MgCuZn based ferrite having the composition ofFe₂O₃ of 40 to 51 mol %, CuO of 5 to 30 mol %, ZnO of 0.5 to 35 mol %and MgO of 5 to 50 mol %.
 5. United multilayer ferrite componentscomprising: multilayer capacitor components including a plurality ofdielectric layers and internal electrodes which are alternatelylaminated each other; multilayer inductor components including aplurality of magnetic ferrite layers and internal electrodes which arealternately laminated each other; external electrodes electricallyconnected to said internal electrodes of said multilayer capacitorcomponents and said mutilayer inductor components; wherein the magneticferrite layers of said multilayer inductor components are composed ofsintered MgCuZn based magnetic ferrite of the magnetostriction being10×10⁻⁶ or lower, and said external electrode is composed of Ag or Agalloys.
 6. The multilayer ferrite components as set forth in claim 5,wherein said sintered MgCuZn based magnetic ferrite has the compositionof Fe₂O₃ of 45 to 49.8 mol %, CuO of 7 to 30 mol %, ZnO of 15 to 25 mol% and MgO of 5 to 35 mol %.
 7. The multilayer ferrite components as setforth in claim 5, wherein said sintered MgCuZn based magnetic ferritehas the composition of Fe₂O₃ of 45 to 49.8 mol %, CuO of 7 to 30 mol %,ZnO of 15 to 25 mol % and MgO+NiO of 5 to 35 mol %.